To achieve high levels of efficiency with a high output at the same time, gas turbines are operated with an extremely high inlet temperature, which often exceeds the permissible material temperature of turbine blading. It is essential to strengthen the bearing working temperature ability of the turbine blade, and to use certain cooling strategies to make it possible nevertheless for the blades to be operated reliably and with long life-time. Development in cooling technique resulted in complicated cooling scheme, multiple (104-106) fine-shaped holes (0.3-1.2 mm) with divergent oblique angles)(10°-75° exist on such air-cooled components in which cooling air flows through the airfoil and discharged through cooling holes. Consequently, the flow of the cooling fluid as a film is determined considerably by the shape and location of the hole, which means the cooling holes need to be straight, accurate, and exactly positioned. For example, diametrical tolerances for air-cooled holes are generally on the order of approximately ±0.002 inch (±0.05 mm) or less.
A wide variety of methods in the state-of-art for producing drilled cooling holes for gas turbine blades, for instance, or in other embodiments, precision drilling techniques such as the laser beam machining, the electrical discharge machining (EDM), and the electrical discharge machining (ECM), etc., are typically used to producing the holes. Specifically, ultrashort pulsed lasers for developing in cooling holes drilling applications with minimized recast layer and negligible heat-affected zone are widely used.
Although the methods for cooling holes drilling known from the state of art have a significant performance on drilling the holes with high efficiency, trial-and-error methods are still implemented in drilling operations. Firstly it is because the actual wall thickness at the designed location of drilled holes deviates from the ideal wall thickness due to the fact that the components such as gas turbine blades with intricate geometry and tight tolerances are often fabricated by investment casting, which is a multiplex nonlinear physical processes coupled with geometry, material properties and boundary conditions. The component, in the embodiment of gas turbine blades, the dimensions produced exhibit non-uniform deformation due to the deformation of wax pattern, expansion of shell, and alloy shrinkage. In addition, holding a thin-walled components such as blades with sculptured surfaces firmly depends on the fixture. Once the turbine blade is localized thoroughly, and restrained by the locators and clamp of the fixture, the component is processed to generate drilled holes with geometric features according to the cooling requirements. In general, the hole feature may have deviation in terms of the localization error. Furthermore, the deviation may occur when clamping the component in the machining process, including the movement and deformation of the component, etc.
As is apparent from the deviations of the ideal drilled holes features discussed above regarding the geometries and positions of drilled hole, the defects such as the occurrence of blind holes, laser burns on the opposite wall, as well as the lack of consistency accuracy of holes. This causes a change in the through-flow of the cooling fluid in comparison with the intended through-flow.
Document U.S. Pat. No. 0,229,759A1 describes a method for the parametric production of a drilled hole in a component, particularly in a gas turbine blade, comprising the steps of: Measuring an actual wall thickness of the component at the location of drill hole; Adjusting the wall thickness on the basis of adjusted parametric drilled hole geometrical value according to measurement. As such, the actual wall thickness of drilled holes can be determined based on the corrected value.
Document U.S. Pat. No. 0,183,325 A1 discloses a method for producing holes in a component, in particular of turbo-machines. The method utilizes 3D model of the actual geometry of the component, adopting each hole on the basis of actual geometry, then the production program is generated for each individual hole. As a result, the process quality and the quality of the holes can be improved.
Document U.S. Pat. No. 6,339,879 B1 teaches a method of sizing and forming a cooling hole in a gas turbine engine component. The method generally entails drilling a hole in the surface of a component, then measuring the thickness of the recast layer surrounding the hole. The thickness of the additive layer of the diffusion coating that will deposit on a corresponding recast surface of the component can be predicted based on an inverse relationship determined by the measured thickness of the recast layer during drilling process. As a result, an appropriately-oversized hole can then be formed in the component.
Although these documents teach various methods for producing drilled hole or drilled holes in a gas turbine blade, or the like, there is no intent to establish, or knowledge about the method for producing drilled holes parametrically in a gas turbine engine component with accurate geometrical and positional values with the consideration of the deviations generated before and after machining.
In view of the above, it would be desirable if an improved process were available for producing the cooling holes of gas turbine engine components with the accurate geometrical and positional parameters.